Project 1, headed by Dr. Fabio Cominelli, will focus on the role of N0D2 signaling and MDP responses in the pathogenesis of experimental CD. It is unknown whether functional abnormalities in N0D2 signaling and MDP responses may lead to chronic intestinal inflammation in CD. We have generated exciting preliminary results showing that SAMP mice with CD-like ileitis (but lacking the N0D2 mutation) display a functional deficit of epithelial innate immunity as well as an abnormal response to MDP that precede the onset of ileitis, suggesting that a defect in innate immunity may have a causative role in this model. The central hypothesis of Project 1 is that functional abnormalities in MDP/N0D2 signaling may cause an aberrant production of innate cytokines, leading to the chronic ileitis in these mice. To test this hypothesis we will: 1) Determine the effects of MDP administration in experimental CD. We will perform a series of in vivo and in vitro experiments to precisely determine the pathophysiological function of N0D2 signaling in SAMP ileitis, SAMP ileocolitis, and TNFDeltaARE mice with experimental CD. Cytokine responses to MDP stimulation will also be performed in a variety of intestinal mucosal cells to define the mechanism of abnormal N0D2 signaling in experimental IBD. 2) Determine the effects of NOD2 genetic manipulation in experimental CD. Using a series of cross-breeding experiments with our SAMP and TNFDeltaARE mice, we will define the role of N0D2 in eariy vs. late phases of chronic ileitis. Finally, by a series of bone marrow chimera experiments, we will determine the contribution of hematopoietic and epithelial-derived N0D2 signaling in mediating CD-like ileitis. 3) Determine the effects of N0D2 pharmacological manipulation in experimental CD. We will determine the effects of pharmacological inhibition of NOD2 signaling on known cellular effects of N0D2 activation and on in vivo ileitis development. Through these specific aims. Project 1 will systematically evaluate the role of MDP and N0D2 signaling in mediating the CD-like pathology found in SAMP and TNFDeltaARE mice. RELEVANCE (See instructions): CD affects more than 500,000 individuals in the US and incurs significant costs to society. Understanding the precise mechanisms and immune defects that cause the disease will allow us to develop better therapies and begin to develop a cure for this devastating disease.